Exemplary embodiments of the invention relate to a method for operating an exhaust gas system of a motor vehicle and an exhaust gas system for an internal combustion engine of a motor vehicle.
Methods and exhaust gas systems are generally well known from the serial production of motor vehicles. Exhaust gas from the internal combustion engine may flow through such an exhaust gas system for an internal combustion engine of a motor vehicle, which includes at least one oxidation catalytic converter and at least one particle filter situated downstream from the oxidation catalytic converter in the direction of flow of the exhaust gas. The oxidation catalytic converter is used for oxidizing constituents of the exhaust gas, in particular for oxidizing uncombusted hydrocarbons and carbon monoxide in the exhaust gas. Nitric oxide in the exhaust gas may also be oxidized by the oxidation catalytic converter. The particle filter is used for at least partially filtering from the exhaust gas particles, in particular soot particles, contained in the exhaust gas.
Due to the filtering of the particles from the exhaust gas, the particle filter becomes occupied with particles, which is customarily referred to as loading of the particle filter. As the result of filtering the particles, the loading of the particle filter with particles from the exhaust gas increases, which is accompanied by a rising exhaust gas back pressure for the internal combustion engine. To minimize the exhaust gas back pressure, and thus, the accompanying disadvantages, it is known to reduce the loading of the particle filter by carrying out a so-called regeneration of the particle filter. For this purpose, the temperature of the exhaust gas is increased by appropriate measures, for example, so that the particles in the particle filter are burned off. For carrying out the regeneration, a control device, for example, is provided by means of which the regeneration is to be performed in a controlled or regulated manner. In other words, the control device is used to control or regulate, and thus carry out, the regeneration.
It has been shown that such methods and such exhaust gas systems have additional potential for further reducing pollutants contained in the exhaust gas, and thus pollutant emissions, by appropriate exhaust gas aftertreatment.
Exemplary embodiments of the present invention, therefore, are directed to an improved method and exhaust gas system that achieves a particularly low pollutant emissions.
According to the invention the regeneration of the particle filter is carried out as a function of at least one aging value characterizing an aging condition of the oxidation catalytic converter. The loading of the particle filter may thus be adapted to the aging condition of the oxidation catalytic converter, by means of which the behavior of the particle filter or its contribution to the aftertreatment of the exhaust gas from the internal combustion engine is adapted to the aging condition. It is thus possible to appropriately adapt and adjust the exhaust gas with regard to its composition or its constituents downstream from the particle filter, so that its composition is favorable, for example, for any further aftertreatment by means of at least one exhaust gas aftertreatment element situated downstream from the particle filter.
The aftertreatment of the exhaust gas achieved by the particle filter has a particularly advantageous effect on the composition of the exhaust gas when, as the result of carrying out the regeneration as a function of the aging value, a loading value that characterizes the loading of the particle filter is set that is greater than a predefinable threshold value. The threshold value is not negative, and preferably is greater than 0.
In another advantageous embodiment of the invention, as the threshold value a constant threshold value is used that is in a range of 1 gram of particles per liter of filter volume of the particle filter up to and including 3 grams of particles per liter of filter volume of the particle filter. The loading of the particle filter has a particularly advantageous effect on the aftertreatment of the exhaust gas by the particle filter, and thus on the composition of the exhaust gas, when the predefinable threshold value is at least essentially 1.5 grams of particles per liter of filter volume of the particle filter. The level of effort for the measurement and/or the computation for carrying out the method may be kept low by using the constant threshold value.
It has been shown to be particularly advantageous when, as the threshold value, a variable threshold value is used that is predefined as a function of the aging condition of the oxidation catalytic converter, in particular as a function of the aging value. In other words, the variable threshold value is dynamically adapted to the aging condition, which changes over the operating life, so that as a result, the loading of the particle filter may also be precisely adapted to the aging condition as needed.
In another advantageous embodiment of the invention, the variable threshold value is predefined from a range of 1 gram of particles per liter of filter volume of the particle filter up to and including 3 grams of particles per liter of filter volume of the particle filter. In this range, the composition of the exhaust gas is influenced in a particularly advantageous manner by the exhaust gas aftertreatment achieved by the particle filter.
One variable that is particularly meaningful and that precisely represents the aging condition of the oxidation catalytic converter is a thermal load on the oxidation catalytic converter within a predefinable time period. In other words, a load value characterizing the thermal load on the oxidation catalytic converter within the predefinable time period is used as the aging value characterizing the aging condition of the oxidation catalytic converter. Alternatively or additionally, an activity value characterizing an activity, associated with the oxidation catalytic converter, for forming nitrogen dioxide in the exhaust gas is used as the aging value characterizing the aging condition. In addition, conclusions may also thus be drawn in a particularly precise manner concerning the aging condition of the oxidation catalytic converter, and thus its capability or tendency to form nitrogen dioxide in the exhaust gas. The loading of the particle filter, and thus its behavior with regard to the exhaust gas aftertreatment, may thus be precisely adapted to the aging condition.
The activity value is preferably determined as a function of a nitrogen dioxide component in the exhaust gas, downstream from the oxidation catalytic converter and upstream from the particle filter, which is achieved by the oxidation catalytic converter. It is thus possible to precisely determine the activity of the oxidation catalytic converter with regard to the formation of nitrogen dioxide, and thus to draw conclusions concerning its aging condition.
In one particularly advantageous embodiment of the invention, a particle filter is used that is at least partially provided with a coating that is active for a selective catalytic reduction reaction of nitrogen oxides in the exhaust gas. It has surprisingly been found that a particle filter which is loaded with particles or soot and at least partially provided with the mentioned coating (selective catalytic reduction (SCR) coating), with an appropriate particle loading and an appropriate temperature range, has an improved conversion of nitrogen oxides in the exhaust gas in order to denox the exhaust gas when there is a comparatively high concentration of nitrogen dioxide in the exhaust gas, compared to a particle filter which is not loaded with particles.
In other words, compared to a particle filter that is not loaded with particles and provided with the SCR coating, the particle filter that is loaded with particles and provided with the SCR coating is able to make a greater contribution to denoxification of the exhaust gas, i.e., for converting nitrogen oxides into nitrogen and water, so that pollutant emissions may be kept particularly low. In addition, it is thus possible to supply the exhaust gas aftertreatment element, possibly situated downstream from the particle filter, with an advantageous nitric oxide component in the exhaust gas, and in particular with an advantageous ratio of nitrogen dioxide to nitric oxide in the exhaust gas, so that, for example, particularly advantageous further denoxification of the exhaust gas may take place by means of the downstream exhaust gas aftertreatment element. The downstream exhaust gas aftertreatment element is preferably an SCR catalytic converter, by means of which the exhaust gas is to be denoxed by carrying out the selective catalytic reduction reaction.
The second aspect of the invention relates to an exhaust gas system for achieving particularly low pollutant emissions, which includes a control device designed to carry out the regeneration of the particle filter as a function of at least one aging value characterizing an aging condition of the oxidation catalytic converter. Advantageous embodiments of the method according to the invention are to be regarded as advantageous embodiments of the exhaust gas system according to the invention, and vice versa.
The pollutant emissions may be kept particularly low when the particle filter is at least partially provided with a coating that is active for a selective catalytic reduction reaction of nitrogen oxides in the exhaust gas, and/or when a catalytic converter for carrying out a selective catalytic reduction reaction of nitrogen oxides in the exhaust gas is situated downstream from the particle filter, a metering device being situated downstream from the oxidation catalytic converter and upstream from the particle filter, by means of which a reducing agent for the selective catalytic reduction reaction is introducible into the exhaust gas.
The reducing agent is an aqueous urea solution in particular. The reducing agent is an ammonia source by means of which, for example in the particle filter provided with the SCR coating and in particular in the SCR catalytic converter, nitrogen oxides are convertible into water and nitrogen, thus denoxing the exhaust gas.
Further advantages, features, and particulars of the invention result from the following description of preferred exemplary embodiments and with reference to the drawings. The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of the figures and/or only shown in the figures may be used not only in the particular stated combination, but also in other combinations or alone without departing from the scope of the invention.